Process for treating cotton material to increase elasticity and elastic recovery



United States Patent 3,441,471 PROCESS FOR TREATING COTTON MATERIAL TO INCREASE ELASTICITY AND ELASTIC RECOVERY I Felix Manor, 143 Hayarkon St., Tel-Aviv, Israel No Drawing. Filed Sept. 21, 1964, Ser. No. 398,657 Claims priority, application Israel, Sept. 27, 1963, 19,990; Nov. 11, 1963, 20,218; Jan. 8, 1964,

Int. (:1. D21c 3/02 US. Cl. 162-90 7 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a process for the treatment of cotton materials produced from cotton fibres, including cotton goods, such as yarns, woven and knitted goods, etc., for improving its elasticity, elastic recovery and other properties, and particularly, but not solely, for increasing its utility for use as stretchable material.

The demand for stretchable material has been steadily increasing during the last years, mainly because of the rapid developing technology with respect to synthetic fibres. This demand has also stimulated research and development work in the natural fibres, particularly cotton, in an attempt to impart to them the new properties with respect to stretchability attained in the synthetic fibres.

In the field of cotton materials produced from cotton fibres, considerable work has been directed to slack mercerizing techniques, in which the material is treated with an alkali while in the slack condition. Slack mercerizing has so far been found to provide a very limited recovery of the cotton fibre after stretching. To increase recovery, further techniques have been devised which fix the fibres in the shrunken state either by heat treatment or by resin cross-linking. The latter techniques increase recovery to some extent, but still short of what would be desired for producing commercially acceptable cotton useful as a stretchable material. Moreover, the latter techniques tend to reduce the tensile strength of the cotton fibre to such an extent that practical applications are still quite limited.

For example, the following data was published as late as May, 1963, comparing properties produced by the foregoing techniques for processing cotton with that obtainable with nylon, this data having been published by the Southern Regional Research Laboratory of the US. Department of Agriculture in Textile Mercury and Argus in May 1963:

3,441,471 Patented Apr. 29, 1969 An object of the present invention is to provide a method of treating cotton to impart improved characteristics thereto with respect to one or more of the abovementioned properties.

A further object of the present invention is to provide a method of treating cotton which will increase its utility as a stretchable material.

The nature of the cotton fibre has been extensively investigated. It has been found to consist of a primary wall containing cellulosic and non-cellulosic substances; a secondary wall in the form of many lamellae or layers of mainly cellulose; and a tertiary wall Within the lumen, which is the residue of the central canal originally containing the growth forming substances of the cotton fibre cell and through which the nutrient substances were fed to the fibre during the growth and development stages.

The cellulose in the primary wall appears to be in the form of a woven net-work of minute cellulosic fibrils and a matrix of non-cellulosic substances. Investigation indicates that approximately 50% of the primary wall is cellulose, the matrix substances consisting essentially of wax (8%), pe tic substances (10%), and nitrogenous material (13%, expressed as protein).

The lamellae layers in the secondary Wall, frequently called the day-growth-rings, consist of dense cellulosic fibrils, these rings usually numbering from 15-30. Such a ring is formed only if and when the temperature is above 30 C. and there is sunlight, and its formation appears to terminate when the temperature drops below 30 C., or when there is no sunlight. Thus the daygrowth-rings appear as distinct layers of cellulose formed during the day when the temperature is over 30 C., each layer being separated by an intervening layer formed at night or when the temperature is below 30 C.

It is generally assumed that the chemical composition of the cotton fibre conforms to that as indicated in the publication of the United States Department of Agriculture AIC6l-(l944) as follows:

Whole fibre Primary wall Constituents percent percent C ellulose 94. 0 54 Protein (N X 6.25) 1.3 14 Pectin substances 1. 2 9 Wax (alcohol soluble 0.6 8 s 3 Cutin/Suberin 4 It was assumed also that the chemical compositions of the day-growth-rings and of the intervening layers formed at lower temperature were identical and that there was only a difference in density. This assumption, however, seems inconsistent with the different reactions to swelling agents and the diiferent dye-stuff absorption. Moreover, the chemical analysis does not conform with my planimetric measurements of the enlarged microscopic photos of the fibre cross-section, wherein I arrived at the following chemical composition (dry condition, approximate).

Primary wall Intervening rings Day-growth rings percent of percent of percent of percent of percent of percent of Whole the priwhole interven. whole day-gr. whole Constituents fibre mary wall fibre rings fibre rings fibre Cellulose 94 54 4 32 1. 3 100 88. 7 Wax 0. 6 8 0. 6 Matrix substances... 5. 4 38 This analysis corresponds to the different properties of the day-growth-rings and the matrix rings, and the percentages approximately conform to the results of extraction of the non-cellulosic substances from the primary wall alone or from the whole fibre.

This analysis explains as well as the specific properties of the cotton fibre, especially the high secondary creep (permanent deformation by plastic flow after continued elongation), therefore the bad elastic recovery (45% after elongation) and the low wrinkle resistance.

The alkali treatment heretofore applied during mercerizing apparently causes an intrafibrillar swelling of the cellulose in the day-growth-rings, i.e., in the substance which alone in the fibre is able to produce real elasticity. However, the alkali treatment appears to cause also an interfibrillar swelling of the non-cellulosic matrix substances which, is is believed, counteracts and restricts the former swelling and therefore limits the elastic properties of the day-growth-rings and additionally limits the elastic recovery by slippage of the swollen plastic gel substances.

It is believed that the presence of this matrix substance in the intervening layers limits the amount of shrinking of the microfibrils inthese layers and especially in the daygrowth-rings and therefore limits the maximum elasticity of the fibre after it has been shrunk by the alkali treatment.

It is also believed that the non-cellulosic matrix substances cause the fibres to slide, upon stretching under stress, and to permanently elongate, and therefore its presence at the time of the alkali-swelling treatment limits the amount of recovery in the processed fibre.

As far as I am aware, while there have been a number of developments for extracting the non-cellulosic substances in the primary wall of the fibre, no one has yet appreciated the above effects in the presence of the noncellulosic matrix substances in the layers between the daygrowth-rings underlying the primary wall, and the advantages in extracting them before the alkali-shrinking treatment.

My invention has for one of its principle purposes the elimination of the sliding within the fibre and the counteracting swelling force by extracting substantially all the non-cellulosie matrix substances not only from the primary wall but also between the day-growth-rings of the fibres before the cotton material is subjected to the mercerizing bath. The latter treatment then swells the microfibrils and bonds together the day-growth-rings, which thereby produces the improved properties in the material.

According to yet another aspect of the invention, after extraction of the non-cellulosic matrix substances the material is heated to a temperature of between 110 C. and 190 C. This imparts improved properties to the material as will be described below.

I have found that when the non-cellulosic matrix substances are extracted from the intervening layers, this provides a looser network of microfibrils in the day-growthrings, enabling them to shrink to a greater extent in the subsequent alkali treatment, thereb yincreasing the elasticity in the processed fibre; and, further, that the subsequent alkali treatment of shrinking bonds the microfibrils together, thereby increasing the tensile strength and resilience of the processed fibre and making resin crosslinking unnecessary.

Tests with the so treated cotton material indicate that the permanent cell elongation by sliding at continuous stress is eliminated and is replaced by a natural elasticity with good recovery. In any event, it appears that the microfibrils in the primary wall are bonded to those in the outermost layer in the day-growth-rings, and also that the microfibrils in the adjacent day-growth-rings are bonded to each other. Apparently, the fibre shrinks more than usual in length in the subsequent alkali treatment and the chains of microfibrils expand from the day-growthrings unhindered into the loose network between them, which explains the bonding between the day-groWth-rings. Thus a natural cross-linking occurs which increases tensile strength and resilience (recovery) without the damaging elfects of resin cross-linking. As most of the noncellulosic substances are extracted, bleaching and dyestuff absorption is also improved.

In extracting the non-cellulosic substances from the primary wall and from the matrix rings between the daygrowth-rings it is preferable to treat the cotton material first for an extended period of time in boiling water and then in a weak alkaline solution. Preferably, it is subsequently treated in a weak acid solution and then again in boiling water.

More particularly, according to the preferred embodiments of the invention the material is treated in boiling water for a period of about 4-10 hours for extraction of part of the wax, gums and slimes and of the water soluble pectin and protein substances. Then the material is treated in a boiling solution of 0.05 to 0.5% of sodium hydroxide for dissolving the hemi-celluloses. The material is then treated with a weak solution of 0.02 to 0.2% of hydrochloric acid for converting protopectins into water soluble pectins and is finally boiled for several hours in water for extraction of the remaining substances.

Following the extraction of the non-cellulosic matrix substances, the cotton material is then subjected to a mercerizing bath. If high resilience (i.e. the ability to absorb work without suffering permanent deformation) is desired in the cotton material, to permit its use as a stretchable material, the mercerizing step would be performed while the material is under slack condition (in accordance with the well-known slack mercerizing procedures), so that the microfibrils can freely change from the crystallite alignment into the zigzag form, which causes high shrinkage. Contrary to the usual slack mercerizing process, this change is now not hindered by the counteracting force of the matrix swelling.

The common commercial procedures utilize a 25% sodium hydroxide solution, as weaker solutions cannot penetrate in the fibres and therefore cannot produce satisfactorily results. As the fibres after extraction of the matrix substances show a high absorption of the sodium hydroxide, it is possible in my process to use the most suitable solution for optimum shrinkage. It is possible to apply any solution from 11% to 32% at 0 to 50 C., depending upon the combination of properties desired in the finished product.

However, I prefer to use in this process a mercerizing bath of 1 1% sodium hydroxide at 0" C., and I have found that this produces more shrinkage, which is probably be cause of the looser structure obtained by extracting the matrix substances.

If, instead of stretch, it is desired to enhance the crease resistance, wrinkle resistance and/ or dimensional stability properties of the material, the mercerizing step would be performed while the cotton material is under tension, an 18% sodium hydroxide solution at 0 C. having been found very suitable.

As discussed earlier, the shrinking of the fibres when subjected to the mercerizing bath into the loose net-work of microfibrils, resulting after the extraction of the noncellulosic matrix substances, appears to produce a natural cross-linking between the different layers which increases the tensile strength and resilience of the material. An additional cross-linking can be applied by treatment with low concentration alkali at sub-freezing temperatures. This treatment is known for viscose-rayon production. Natural cotton fibre cannot be bonded together in such a solution, but fibres from which most of the non-cellulosic substances were extracted according to the above description can be bonded or cross-linked in this way.

When this sub-freezing alkaline treatment is used in the described process, it is preferable to use a 4% sodium hydroxide solution at C. in both of the abovedescribed procedures.

In the slack mercerizing procedure, the additional steps of neutralizing, scouring, dyeing and finishing would also be applied as usual for stretch goods. In the tension mercerizing procedure, the additional step of neutralizing, dyeing or bleaching and finishing would also be applied as usual for goods of this type.

Following are several examples of processes of treating cotton fibre in accordance with the present invention.

EXAMPLE 1 This example used a specimen of cotten cloth, grey material, cotton battist Ne 40/40 combed, TM 4.-, 79/56 per inch; (cover factor 12 /2 /9; total"21 /z).

The above specimen of cotton cloth was first desized, and then the non-cellulosic matrix substances were removed by the following treatment: The sample was treated in boiling water for one hour; the water was changed, treated in boiling water for a second hour; and for two further one-hour periods (or a total of four hours) with a water change between each period. The sample was then treated in boiling /2% solution of sodium hydroxide for three one-hour periods with a solution change between each period. Then the sample was treated in boiling water for four one-hour periods with a water change between each period. The sample was then air dried. The sample was then subjected to a slack mercerizing process by treating it in a 15% sodium hydroxide solution at 25 C. for ten minutes. Additional cross-linking was then provided by the sub-freezing treatment described earlier, by subjecting the sample to a 4% sodium hydroxide solution at l0 C. for minutes. The sample was then neutralized with dilute acetic acid, scoured and dried.

The results observed in the sample so treated are as follows: Shrinkage to 94/ 86 /2 ends per inch (cover factor 15/ 13 /2; total 28 /2); single yarn strength increase 22% to 16g/tex; stretchability warp-wise 15%, 97% recovery; fillingwise 25% with 96% recovery.

EXAMPLE 2 The following treatment was applied to a sample of cotton hosiery having the following characteristics: Grey materials: Cotton hosiery from 24/1 carded yarn with TM. 2.8.

The non-cellulosic matrix substances were extracted by treating the sample for four one-hour periods in boiling water with a water change between each period. Then the sample was treated in boiling 0.05% sodium hydroxide solution for two one-hour periods with a solution change between each period. The sample was then treated with 0.02% hydrochloric acid for half an hour and finally boiled for four one-hour periods with a water change between each period. After air-drying the sample was slack mercerized by treating it in an 11% sodium hydroxide solution at 0 C. for ten minutes. Neutralizing the sample was effected by dilute acetic acid, and the sample was then dried. Additional cross-linking between the fibres was then imparted to the sample by treating it in a 4% sodium hydroxide solution at -10 C. for minutes, followed by neutralizing in boiling water and drying. The sample thus treated indicated a stretchability of 70%, with recovery.

It has been found that an improved method of crosslinking can be effected by applying pressure to the cotton after it has been treated in the mercerizing bath and before it has dried. This new method is an alternative to the sub-freezing alkaline treatment method described above.

The pressure treatment for effecting cross-linking is performed after the cotton material has been subjected to the mercerizing bath, either while the cotton is still soaked with the alkaline solution, or soaked with alkaline solution diluted to l%5%; or after washing out the alkaline solution, but in any case before drying.

Preferably, the pressure should be between 25 kg. and 500 kg. per square cm. The pressure can be applied for fabrics by wet calendering, and for yarns or for knit goods by a mechanical press. The pressure may be applied under normal room temperature, but it is preferable to heat the pressure applicator to a temperature of between C. and 220 C.

The purpose of application of pressure is to increase the area of surface contact between the cotton fibres thus factilitation the bonding between them. The purpose of heat is the setting of the fibre position and the recovery of the natural fibre-crimp which was straightened by the stress of the production processes.

EXAMPLE 3 As an example of the improved method of cross-linking by pressure, a speciment of cotton cloth was treated in accordance with Example 1 above, except that instead of effecting the cross-linking by the sub-freezing alkaline treatment, the specimen, after it left the mercerizing bath and while still wet, was subjected to a pressure of about 100 kg. per sq. cm. by a mechanical press heated to a temperature of C. It was found that additional crosslinking was produced by this step.

'It has further been found that the cotton material, after extraction of the non-cellulosic substances according to the above-described process, can sustain far higher temperatures than material containing the non-cellulosic substances; and that when it is subjected to these higher temperatures, remarkably improved properties are produced. Cotton materials in which the non-cellulosic substances had not been extracted could not sustain these higher temperatures as they started to yellow and to weaken at temperatures over 110 C. This is believed to be due to the denaturation of proteins and changes of pectins which occur at the higher temperatures, these materials being present in the non-cellulosic sub-stances. However, when these substances are removed with the other non cellulosic materials in the above-described process, it was found that these effects of yellowing and weakening were absent, and that remarkably improved properties were imparted to the cotton.

It is not known with certainty exactly how heating the cotton material at the temperature and time periods stated above, after extracting the non-cellulosic substances and before subjecting to the alkaline bath, produces the changed properties in the cotton. Apparently, strong heat treatment imparts to the cotton fibres a crimp, possibly by reactivating the natural .fibre crimp which was straightened during the processing; and the subsequent alkaline treatment fixes this crimp in such a way that the treated goods shrink more than usual and acquire a substantially higher elasticity and elastic recovery. The heat treatment is between 110 C. and C., and is preferably for a period of between 10 minutes and 3 hours. Heat-treatment in the lower range of temperatures imparts higher strength and increased resistance against acids and alkali, which might be due to changes in the cellulose chains. Because of this increased resistance to alkalis it is preferable that the subsequent alkaline mercerizing bath be somewhat more concentrated than that in the above-described examples. Solutions of l3%-43% sodium hydroxide have been found quite satisfactory; and concentrated alkaline solutions in which the alkaline is present in the vicinity of its saturation point i.e. about 43%, (at room temperature) are preferable.

It has also been found that additional improvements can be imparted to the cotton by subjecting it to an additional heat-treatment following the alkaline treatment. This additional heat-treatment is preferably between 110 C. and 190 C. for a period of between minutes and 3 hours.

Following are three examples of processes of treating cotton fibres in accordance with the foregoing aspect of the present invention:

EXAMPLE 4 This example used a specimen of knitted cotton from combed Ne 40/1 T.M. 2.9.

The specimen was treated for 4 hours in boiling water, 2 hours in boiling NaOH solution, 1 hour in boiling water, 10 minutes in 0.1% sodium hyperchlorite at 60 C., and 1 hour in boiling water. The sample was then for 30 minutes heated to 175 C., subjected for 30 minutes to 35% NaOH (at room temperature), neutralized in diluted acetic acid, scoured, and subjected to a second heat treatment of 1 hour at 175 C.

The resulting product had the following elongation and elastic recovery properties:

Immediate elastic recovery, percent Elongation, percent First cycle Second cycle Delayed elastic recovery after 30 minutes: 100%.

EXAMPLE 5 EXAMPLE 6 This example used a specimen of cotton gauze from Ne /1 carded; 28/16 ends per inch, cover factor 6.3/3.6 total 9.9.

The specimen was treated for extraction of non-cellulosic substances as described in Example 1, heat-treated for 30 minutes at 175 C., subjected to a NaOH bath of 43% at C. (i.e. at saturation point), scoured, boiled and heat-treated for minutes at 150 C.

The treatment resulted in a shrinkage to 50/33 ends per inch, i.e. cover factor 11.2/7.4 total 18.6. The immediate recovery after elongation showed as follows:

Immediate elastic recovery, percent Elongation, percent First cycle Second cycle Delayed elastic recovery after 30' minutes:

It is to be understood that described embodiments of this invention are illustrative only, and that the invention may be applied in other forms and applications, and is therefore to be limited only as defined in the following claims.

I claim:

1. A method of treating cotton material produced from cotton fibre for purposes of increasing its elasticity and elastic recovery properties, comprising, extraciing non-cellulosic matrix substances from the primary wall of the cotton fibre and from the layers between the daygrowth-rings underlying the primary wall, heating the cotton material to a temperature of between C. and C., and then subjecting the cotton material to a mercerizing bath.

2. The method as defined in claim 1, wherein said mercerizing bath is a 13-43% sodium hydroxide solution.

3. The method as defined in claim 1, wherein said mercerizing bath is a concentrated alkaline solution in which the alkali is present in the vicinity of its saturation point.

4. The method as defined in claim 1, wherein the noncellulosic matrix substances are extracted by heating the cotton material in boiling water and then treating same in a weak alkaline solution.

5. The method as defined in claim 1, wherein the noncellulosic matrix substances are extracted by treating the cotton material in boiling water for a period of 4-10 hours, and then treating same in a boiling solution of 0.05% to 0.5% sodium hydroxide by weight for a period of 2-4 hours.

6. The method as defined in claim 5, wherein the cotton material is treated, after said treatment in said boiling solution of sodium hydroxide, in a weak acid solution for a period of one-half to two hours.

7. The method as defined in claim 6, wherein the cotton material is treated in boiling water for an additional period of 26 hours following said weak acid solution treatment.

References Cited UNITED STATES PATENTS 858,411 7/1907 McFarland 16295 2,108,125 2/1938 Hoddeson 16290 X 2,126,809 8/1938 Pratt 8125 2,179,505 1l/l939 Huey 8l25 2,205,120 6/1940 Heberlein 8125 X 2,528,793 11/1950 Secrist, 2,646,341 7/1953 Fetscher 8-125 2,769,685 1l/1956 Cowles 8-125 2,970,882 2/1961 Kumin 8l25 X HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 

